beginabstract In custom software development projects, it is frequently the case that the same type of software is being built for different customers. The deliverables are similar because they address the same market (e.g., Telecom, Banking) or have similar functions or both. However, most organisations do not take advantage of this similarity and conduct each project from scratch leading to lesser margins and lower quality. Our key observation is that the similarity among the projects alludes to the existence of a veritable domain of discourse whose ontology, if created, would make the similarity across the projects explicit. Design diagrams are an integral part of any commercial software project deliverables as they document crucial facets of the software solution. We propose an approach to extract ontological information from UML design diagrams (class and sequence diagrams) and represent it as domain ontology in a convenient representation. This ontology not only helps in developing a better understanding of the domain but also fosters software reuse for future software projects in that domain. Initial results on extracting ontology from thousands of model from public repository show that the created ontologies are accurate and help in better software reuse for new solutions.